To investigate the ideal suture material to intraoperatively test strain at a primary nerve repair site. As 5%-8% strain represents a critical threshold past which nerve ischemia develops, we aimed to determine which readily available suture reliably failed by an average of 5% and a maximum of 8% strain when loaded to failure.

Methods:

19 cadavers were procured. The median nerve was exposed in the distal forearm and neurolysed 15cm proximal to the transverse carpal ligament (TCL), where it was cut and attached to a spring gauge. The nerve was marked at its midpoint and additionally 5cm on either side for later strain measurement. A laceration was then created at the midpoint marking. A single epineural suture was placed performing end-to-end repair without tension. The suture repair site was then loaded to failure while videotaping. Strain measurements at failure were performed. 8 different sutures were tested: 6.0, 8.0, 9.0, and 10.0 Nylon; 6.0, 7.0, 8.0, and 10.0 Prolene.

Results:

The average strain at failure of 9.0 Nylon most closely approximated 5% (4.9%). 8.0 Prolene and 10.0 Nylon and Prolene additionally failed with average strains less than 5% and a maximum strain of failure less than 8% (Figure 1). 6.0 to 8.0 caliber suture irrespective of type failed primarily by pullout of the suture from the epineurium, whereas 9.0 and 10.0 Nylon and Prolene failed by suture breakage (Table 1). Increased variation was seen when testing sutures that failed by pullout from the epineurium.

Discussion:

8.0 Nylon suture has been advocated as the suggested intraoperative aid to test nerve strain at a primary nerve repair site. Our study would however suggest 9.0 Nylon is the most appropriate suture due to its more predictable failure via breakage, as well as its failure by a threshold of 5%-8% strain. While 8.0 Prolene, as well as 10.0 Nylon and Prolene additionally failed by 5-8% strain, 8.0 Prolene was difficult to procure and its failure by pullout is not as reliable.10.0 Nylon and Prolene failed well below 5% strain, which may lead to a high rate of inappropriate abandonment of primary repair. 8.0 Nylon in contrast, failed above the threshold of 5% strain, and via the less reliable mechanism of pullout.

Conclusion:

9.0 Nylon, not 8.0 Nylon, is the most appropriate suture to use when testing strain at primary nerve repair site intraoperatively.